This invention relates to drive fasteners and to a drive fastening system in which the drive fastener is deformed to increase the retention force thereof.
Drive fasteners are well known in the art. A drive fastener comprises an elongated body having an enlarged head which is driven into preformed apertures formed in the articles which are to be fastened together. According to conventional manufacturing techniques, when using a drive fastener to fasten an item to a base, the aperture in the item is sized to present a clearance fit to the fastener, while the aperture in the base is smaller to create an interference fit with the fastener. The interference fit between the base aperture and the fastener creates a retention force which holds the fastener in the aperture and the item to the base.
Drive fasteners may be either rotational or nonrotational. Rotational fasteners are formed with helical splines along the length of the fastener which form complementary threads in the aperture in the base upon the application of a pushing force to the drive fastener head.
A problem arises, however, since the retention force of a rotational drive fastener is related to the number of splines per inch. Since the number of splines per inch is low, the retention force is not as great as a conventional screw. As a result, a rotational drive fastener will fail by counter-rotating out of the self-threaded apertures upon the application of a force to the fastener which is opposite in direction to the insertion force.
Nonrotational drive fasteners are formed with a knurled or ribbed pattern along the length of the fastener which becomes imbedded in the base aperture, or with no pattern at all. Such nonrotational fasteners are susceptible to failure by withdrawing from the base aperture upon an application of a suitable force to the fastener.